text:
Why do so few non-US runways have EMAS beds?
As occurrences of an aircraft running off the end of the runway and hitting things tend to leave both the aircraft and whatever it hits rather the worse for wear, much effort over the years has gone into both preventing runway overruns1 and mitigating the consequences of overruns when they do occur.
There are three main ways of mitigating the consequences of a runway overrun:

Providing a long, clear, flat runway safety area (RSA) past the end of the runway, to allow an overrunning aircraft space in which to safely decelerate, free of the risk of striking anything else; this is highly effective, and the preferred solution for new runways and airports, but requires a considerable length of free area past the runway end, which is often not available at older airports (for instance, due to a runway ending just prior to the airport boundary, with dense residential or commercial development or major roads, rail lines, or waterways immediately adjacent, or due to terrain which drops off steeply past the end of the runway).
Replacing solid objects past the end of the runway with frangible equivalents, which break apart harmlessly when struck by an aircraft instead of standing firm and potentially causing severe damage; this is nearly ubiquitous for airport equipment such as approach lights and radionavigation aids, which, by their very nature, must often be located within the RSA (and usually in the highest-risk portion of the RSA [along the centerline and extending quite close to the end of the runway], at that), but is not practical for structures beyond the airport boundary.
Decelerating an aircraft very quickly, so that it stops before hitting anything solid; this is usually done using an engineered-materials arrestor system (EMAS), generally consisting of a bed of cellular-concrete or foamed-silica blocks which crush under the weight of an aircraft, causing the aircraft’s landing gear to sink into and drag through the EMAS bed and quickly bringing the aircraft to a stop.  EMAS is the preferred solution in instances where terrain or land-acquisition factors make a full-size RSA infeasible.

There are at least 116 EMAS beds and counting at U.S. runway ends, but only 15 or so in the entire rest of the world combined.  This despite the fact that airports which could benefit from EMAS are no less common elsewhere than in the United States; for example (sorted by number of dangerous runway ends):

SBSP runways 17L, 17R, 35L, 35R: Heavy urbanisation and busy roads just past the ends of all of these runways; however, I am not, as of yet, aware of any accidents involving aircraft running off the ends of these runways.2
VOML runways 06, 09, 24, 27: Very steep drop-off past the ends of these runways (the airport is perched on top of a hill); this has resulted in at least one fatal accident.
CYYZ runways 23, 24L, 24R: Deep ravine and creek runs past the ends of the three runways; this has caused at least two accidents over the years.
SCIP runways 10, 28: Steep drop-off past the end of the runway (the slope of the ground falls away below the runway near the end), most prominent for runway 10 but also present (albeit to a considerably lesser degree) for runway 28; fortunately, no accidents yet (of which I am aware).

To the best of my knowledge, none of these runways are equipped with EMAS.3
Why are EMAS installations apparently so rare outside the United States?

1: Methods for doing this include:

Plowing, grooving, and sanding runways to improve traction (and, thus, aircraft braking capability) in adverse weather conditions.
Requiring the use of landing-distance computations based on up-to-date braking reports to ensure that there exists sufficient runway for an aircraft to come to a stop on the paved surface.
Training pilots to promptly apply all available deceleration devices during landing (especially in adverse weather conditions), such as wheelbrakes, spoilers, and reverse thrust.
Preventing unnecessary high-speed rejected takeoffs through better pilot training, including:

Not rejecting for tyre failures except at very low speed
Not rejecting for any reason after V1 unless there is reason to think the aircraft incapable of controlled flight.

Training pilots in the proper technique for rejecting a takeoff if one is necessary, including:

Making a quick, certain go/no-go decision immediately upon experiencing a failure, rather than dithering on whether to reject or not as the aircraft continues to accelerate towards the end of the runway.
Fully applying all available deceleration devices immediately upon making the decision to reject.
Maintaining full application of all deceleration devices until the aircraft comes to a complete stop.

2: There were two accidents, on 16 and 17 July 2007, involving aircraft departing the paved surface of SBSP runways 17R and 35L, respectively, under conditions of heavy rain, the latter of which resulted in 199 fatalities; however, in both of these cases, the aircraft veered off the side of the runway before reaching the end, and, thus, an EMAS, even if installed, would not have prevented these accidents, as EMAS installations generally only cover the ends of the runway, not the sides.
3: The departure end of VOML runway 06 did have a sand-filled arrestor bed; however, it failed to stop the aircraft in the aforementioned fatal accident, while a full-fledged EMAS bed most likely would have prevented the plane from plunging over the precipice.

Too broad. There won't be one single answer to this. There are many reasons why things are done or not done. Think cost, space, lack of regulatory requirement, better return (in terms of lives saved per dollar) from other projects, planning objections...

You realize CYYZ is not in the US no?

@JohnK yes it is, Canada is America's hat! :) :) Neither are the other 3 example airports specifically called out as good potential locations for installation of EMAS.

As a Canuck, I prefer Homer from The Simpsons' term:  "America Light" lol.


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Why do anti-ice systems on airplanes with automatic ice detectors still need to be manually selected on?
As even minuscule amounts of ice accumulation on aircraft can cause tremendous loss of lift, increases in drag, decreases in engine thrust, and/or flight-control impairment, some method of detecting ice is essential for safe flight, even for aircraft not certified for flight into icing conditions.  Various methods exist for doing this, ranging from examination with the Mk. I eyeball (for many light general-aviation craft, and even some larger planes) to sophisticated electromechanical systems utilising vibrating probes which change frequency when made more massive by ice accumulation and set off an alarm in the cockpit.
For aircraft not certified or equipped for flight in icing conditions, the detection of ice lets the flightcrew know that they need to get out of the ice ASAP.  For aircraft which can fly in ice, it signals the need to activate the aircraft’s built-in deice/anti-ice systems; these come in three main varieties (melting the ice using hot engine bleed air, melting it with resistance heating from electrical heating elements, and mechanically breaking it off with pneumatically-operated deicing boots), but all of these still need to be manually turned on by the pilots, even for aircraft that can automatically detect icing.
Given the potentially-catastrophic consequences of allowing ice to accumulate unchecked on an airframe, and the ease with which a flightcrew (especially if fatigued or already task-saturated) could overlook or forget about an ice warning, why don’t aircraft with automatic ice detectors and built-in anti-icing link the two together, and have the ice detector automatically turn on the anti-ice system when it detects icing?

If the detection fails you want to be able to turn it on (so it needs an "ON" switch), similarly you want to be able to turn it off (so it needs an "OFF" switch). So maybe the question should be why don't they have an "ON-OFF-AUTO" switch?

On some aircraft, it does actually work automatically. E.g. on the Boeing 777 both engine and wing anti-ice have an automatic position:

In flight, when an ENGINE ANTI-ICE selector is in AUTO and engine icing conditions exist, the respective engine anti-icing valve is commanded open. [...]
In flight, when the WING ANTI-ICE selector is in AUTO and wing icing conditions exist, the wing anti-icing valves are commanded open.

(Boeing 777 FCOMv2 3.20.1 - Anti-Ice, Rain - System Description)
The 787 and 747-8 also have the auto position. I'm not sure about the 737 MAX.

Airbus does not seem use any automatic system to turn on anti-ice. Even in the A380 and A350, anti-ice needs to be selected manually by the crew. There are of course cautions about detected icing:

If at least one ice detector detects icing conditions, and if engine anti-ice is off: The ECAM triggers
the A-ICE ICE DETECTED caution. [...]
If at least one ice detector subsequently detects severe icing conditions, and if wing anti-ice is off:
The ECAM triggers the A-ICE SEVERE ICE DETECTED caution.

(Airbus A380 FCOM 30-10-10 - Ice and Rain Protection - System Description)

Because most of the time the system has to be on even when there isn't detectable ice accumulation.  Because of what I like call "technical icing conditions" but which are just called "icing conditions":
ICING CONDITIONS:

TAT (total air temperature - accounts for temperature rise from compresibilty) less than 10C

Visible moisture (cloud, haze, anything that is water)

SAT above -40C

You also have to have WAI on for takeoffs when OAT is less than +5C with visible moisture (including visibility under 1 mile) regardless of whether there is actual ice formation (water streaming back on the wing on takeoff can freeze upon rotation due to the temperature drop from the low pressure over the wing).
When you get the wings deiced, you still have to have the WAI on at the start of the takeoff roll if departing in technical (or actual) icing.  You don't want to cook the thick type IV holdover fluid, so you leave WAI on selection the very last thing as you pull out to line up for the TO roll (the CRJ200 has an evaporative WAI system which meant the leading edges get VERY hot, about 105C, which could cook the fluid and make it crusty).
When flying, the only time you can leave the WAI off when in technical icing conditions is
above some speed (on the CRJs it was 230kt), unless you get an ICE caution from the ice detector.
The result is a system that automatically turns the WAI on when ice is detected would only cover about, oh, maybe 10 - 20% of the time you are legally required to have WAI on.
Cowls are similar, but have to be on even more often because there isn't the 230kt threshold for actual accumulations only. They have to be on all the time you are on the ground less than +10C with visible moisture (freezing around cowl inlets from velocity temperature drop).
Without the 230kt exclusion the wings have, you have to have the cowls on pretty much all the time you are in cloud, actual icing or not, so you are turning them on and off quite a lot if climbing/descending through layers (some pilots may just leave them on), whereas outside arrivals and departures the wings are only on when you get actual ice.
So you could automate the system like that, if you could figure out how to make the system reliably detect "visible moisture" outside somehow (probably possible, but very expensive).   Otherwise, the decision to turn it on is a crew decision based on the view outside, probably 80% of the time.

Except that, regardless of anything else, actual icing requires anti-ice, if installed, to be activated, and automating anti-ice activation upon detection of icing wouldn't affect the crew's ability to manually activate the anti-ice system.

You can have a system turn on automatically, and some  airplanes do that, but the point is that it doesn't really mitigate risk. When you get an ICE caution, you turn the wings on right away and you don't really need to automate that activity as a risk mitigation. The risk of an airplane crashing because the crew ignored an ICE caution at normal cruising speeds is vanishingly small. The risks are in the approach/departure phases, in conditions that may not  trigger an ICE caution.  Slat systems are a far greater risk mitigation actually, because they make the plane insensitive to minor icing.

In answer to the question: Many airplanes do have automatically activated anti-ice systems.***

Anti-Ice technology evolves,
Later production airplanes of a type that maybe in production for decades can be markedly different from early ones.
There are also 'Operator chosen' options as automatic anti-ice operation is generally not mandated by the rules.
Different manufacturers can have different systems too.

What I'm trying to say is that similar cockpits may have different combinations of Anti-Ice system operation.
My own airline fleet had it as follows:
The B747-400 (P&W4056)

Wing Anti-ice (WAI) and Nacelle anti-ice (NAI) from engine bleeds.
WAI manual only, NAI auto or manual, on ground only manual NAI.
auto is based on "nacelle icing conditions are detected"
WAI only available in the air in CLEAN configuration (no slats, flaps extended)

B777 (GE90)

Wing Anti-ice (WAI) and Engine anti-ice (EAI) from engine bleeds.
WAI and EAI auto or manual, on ground only manual EAI.
auto is based on "engine icing conditions exist"
WAI only available in the air in CLEAN configuration (no slats, flaps extended)

B787 (GEnx)***

Wing Anti-ice (WAI) is Electrical and
Engine anti-ice (EAI) from engine bleeds**.
WAI and EAI auto or manual, on ground: speed>75kts auto WAI available. only manual EAI.
auto is based on "When icing conditions are detected"
WAI available in the air and on the ground with speed>75kts.

**The left and right engines have identical, independent anti-ice systems as bleeds are not used for cabin Airconditioning and Pressurisation.
*** A completely automated system is the GEnx Ice Crystal Icing 'Function'

Only allowing wing anti-ice when in clean condition seems like asking for trouble, given that unclean conditions are generally those in which the aircraft operates with the least stall margin (and, thus, those in which the effects of icing are potentially the most severe).

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Why does the CF6 have a lower bypass ratio than the TF39?
The General Electric TF39, which powered the original C-5 Galaxy, was the very first high-bypass turbofan brought into mass production, with a previously unheard-of 8:1 bypass ratio.  Yet, when it came time to make a civilian version of the TF39 (what would become known as the General Electric CF6), GE cranked the bypass ratio back to under 6:1 for the lowest-thrust version, and to 5.31:1 or lower for the beefier CF6s.
Why did GE decrease the bypass ratio of their engine, rather than increasing it further?

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Why aren't 737s or A320s commonly used for transatlantic flights?
Despite newer models of the 737 and A320 families having more than enough range to cross the North Atlantic (and also most of the older models, if they refuel at Gander and\or Shannon along the way; the only one for which this isn't the case is the 737-100, which would require an additional fuel stop in Keflavik, and which is, in any case, no longer in service anywhere), 90% of transatlantic passenger flights are by widebody jets, with 757s accounting for most of the remainder; only 1% of transatlantic commercial flights are by smaller narrowbodies like the 737 or A320.
Given that all A320s and all Next Generation\MAX 737s can fly nonstop between the U.S. east coast and western Europe, and that even the older 737s can fly between the U.S. and Europe if they make a stop or two along the way to refuel, why are the smaller narrowbodies so rare in transatlantic flight, when the prospect of using these smaller, cheaper, more flexible (operationally-speaking, that is, not physically more flexible) aircraft to fly passengers across the Atlantic would seem to be very attractive to airlines, especially low-cost airlines (for instance, Southwest or Ryanair)?

The market is large enough to fill in the A330 and B777 and even for thin routes the A321LR might be lacking range. For example it can't cover Eastern Europe to US. However, there are some rumors of possible A321XLR version. Anyway, when new generation of composite narrow bodies (or further range increase of existing models) will arrive, things might change.

Making "a stop... along the way to refuel" is a total deal-breaker, when your competitors aren't doing that. Making "two [stops] along the way to refuel" is two total deal-breakers.

I have flown on an A320 transatlantically. I think it was from Central Europe to New York JFK airport (non-stop) but I ain't sure. Could also have been the one to Chicago O'hare Airport, also non-stop. But I definitely flew on an A320 across the Atlantic ocean once (at other times I flew in a B747 and a B777).

You need to have both a suitable aircraft and a company with the business model to fly the routes.
As to aircraft, only the max8 and a321neo have the range to be really suitable. Westbound in the winter requires additional range that would require a refueling stop in the other models you mention, and that is no way to be profitable on any route. These are both new and in comparatively short supply. The aircraft and operator both need ETOPS ratings.
It is difficult to build a transatlantic business around a particular aircraft if it only just barely has the range for the closest city pair, meaning any expansion requires a second model. Ryanair, Southwest, etc. may not find this attractive.
Widebodies can fly from any US city to any European city. WOW uses the a321neo for the shorter routes, but also has a330s for west coast cities. WOW uses Iceland as a hub, already partway across the Atlantic.
While I think that flying narrowbodies across the Atlantic will grow, just barely good enough for a handful of airlines makes this arrangement unlikely to dominate given the flexibility of the widebody competition.

The MAX 7 has a longer range than the MAX 8 (7130 km versus 6570 km), so if the MAX 8 has the range to be suitable, so does the MAX 7.

@sean Correct, but the MAX7 is an orphan that is unlikely to survive. No one wants to own an unpopular aircraft; it complicates financing, maintenance, resale, etc.

No one... except Southwest Airlines, apparently.  (I wonder if Southwest is thinking about expanding into Europe - that would certainly explain why they're buying at least thirty of the longest-range 737 Boeing offers...)

@Sean Southwest has deferred 24 of its 30 Max7 orders to mid 2020s, apparently trying to decide whether to even keep them. Southwest has the world's largest fleet of 737-700s at 512, but has ordered 251 max8s compared to the 4 undeferred max7s. This is not healthy for the max7.

New question here about why the MAX 7 isn't sellin'.

Update: in the past couple years, Southwest has now massively increased MAX 7 orders.

@Vikki The Max7 has little to do with this answer and Southwest does not fly to Europe. Govt overreaction to Covvid dropped US airline passenger count from 80m/mo to 3m/mo in 1Q20, a monumental decrease that made all airlines look for ways to lower breakeven. Smaller planes are one way.

Two likely reasons:

Economics - If your number of flights per day is limited to 1 or 2 and/or you have a limited number of gate slots available, you're better off (i.e., you'll make more money) maximizing the number of passengers per flight.  A 737-MAX can carry around 200 passengers in a single-class sardine configuration.  A 777 can carry almost 400 passengers in a similarly dense configuration, and over 300 in a more comfortable, multi-class configuration.  A 777 is more expensive than a single 737, but much less expensive than two 737s.
Comfort - As a passenger, I would not want to fly across the ocean in the aforementioned sardine configuration, and would not buy a ticket to do so.  SWA is great for short hops, but anything over a couple of hours starts to get intensely uncomfortable, sometimes painful (I have long legs that start cramping if I can't stretch). You're not going to get a lot of repeat business if your passengers can't walk once they reach their destination.

Offhand, I can't recall ever having been on a trans-Atlantic flight that wasn't pretty nearly full.  Indeed, I've been bumped from a couple that were over-full.  So if the airline can count on generally filling a 747 or 777, why would it fly two 737s?

Why not? Boston-Dublin  isnt much farther than LAX-Cleveland, and people sardine that all the time.

About price that is not really true, for price of one 777 you can get around three 737.

@Harper Dublin to Boston is usually into a beefy headwind and takes seven hours non-stop (BOS-DUB with the tailwind is about six); LA to Cleveland is only four-and-a-half hours. Not even the same ballpark.

@DavidRicherby oh man, I learned that one flying continentally one time, a usually 4+ hour flight was <3hr. We wound up losing it all though, since they had no gates for us until the first 6am departure.  So we sat on the taxiway for an hour.

Some airlines are now starting to do this on routes short enough. Norwegian air now has a route out of Stewart Airport in NY direct to Dublin on a 737-Max8 I flew it late last week and it was quite nice. I believe they have a few others as well direct to Dublin from other northern departure locations in the US.
Traditionally there has always been a fear of flying smaller jets over large stretches of open water and for a long time small twins were not capable of the distances needed.

The question is about why this isn't more common.

Air Canada flies to London on B737-8 too :)

A good design fundamentals and applications study.
First consideration is how much weight how far.  In other words, how one would split fuel load and PAY load.  Over time, even pennies saved here would add up.  Short haul would carry less fuel and more people.
Next up is wing design and power.  The long range plane might gain a few percent in efficiency with smaller, thinner "cruise" wings and fewer turbofans to squeeze out savings in fuel, but not as suited for rapid climbs in shorter, more constricted airspace.
There is also the issue of short field performance.  There a larger wing and more power are desirable.
In the end a bit like comparing a thoroughbred with a quarter horse.  Versatility vs long distance running.
Not that any other aircraft can fly trans-atlantic, but the most efficient will be in the majority.


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Why aren't there aircraft with forward-mounted vertical stabilizers?
Many aircraft have the horizontal stabilizers mounted in front of the main wings (this is called a canard configuration); however, to the best of my knowledge, there don't seem to be any aircraft with vertical stabilizers in front of the wings.
Why is this?

@Peter Kämpf These might be different questions unless a rudder is the same thing as a vertical stabilizer and possibility the same as practicality.

@Pilothead: Calling any surface forward of the center of gravity a stabilizer is a misnomer. It can only stabilise the aircraft when actively and intelligently moved, like a rudder. So yes, a forward-mounted vertical "stabilizer" is a rudder.

@PeterKämpf So then aren't these different questions? Forward mounted vertical stabilizers aren't used because they don't stabilize, and forward mounted rudders can stabilize if actively controlled.

@Pilothead Where's the difference? Since it makes no sense to add a forward "stabilizer", it has not been done (except for pterodactyls and missiles, in a way - they have actively controlled rudders).

Stabilizers create directional stability - they keep the pointy end pointed forward. To do that, they must be mounted behind the rotational pivot point that the aircraft rotates about, the center of gravity.
So when a airfoil or control surface is mounted forward, in front of the center of gravity, (canard), it cannot, by itself, be functionating as a stabilizer, (even though we may refer to it as a stabilizer). It is, in fact, only a horizontal or pitch control surface.
In this case, (a forward mounted canard), the canard is not creating directional stability, the rear-mounted main wing creates this directional stability (pitch stability) about the lateral axis.  The canard itself actually detracts from directional stability. It is there to provide control about the lateral axis.
A vertical stabilizer is there to provide directional stability about the vertical axis (yaw or sideslip stability).  You can't mount a vertical stabilizer forward because there is no other vertical airfoil at the back providing directional stability about the vertical axis. Or perhaps it might be more accurate to say you could, but only if there were a larger vertical stabilizer in the back. In which case it would be pointless to put another one in the front. that would be reducing stability and requiring the rear-mounted one to be bigger.
An example here to illustrate the point might be the AIM-7 sparrow missile. It does have it's horizontal and vertical control surfaces in the front. It has fixed wings at the aft end of the missile (which are the stabilizing airfoils), and movable control surfaces somewhat forward of the C.G. It maintains a constant* roll attitude and can maneuver in any direction (left/right/up/down), without rolling or changing its bank angle. It does this by deflecting the forward control surfaces as necessary to create lift in the desired direction. So, it effectively does have it's horizontal and vertical "stabilizer" (actually, control surfaces) forward of its fixed stabilizing airfoils.
*NOTE. although actually, in the F-4 at least, the AIM-7 was programmed to always initially roll and then maintain a roll attitude where its wings and control surfaces are oriented in an "X" configuration relative to the launch aircraft, not as a "+" the way you might imagine.

From the image you can see that a vertical stabilizer mounted behind the aircraft CG imparts a restoring moment to a yaw disturbance which increases as the yaw movement increases. If the fin were placed on the nose of the aircraft, ahead of the CG, the moment would amplify the yaw disturbance, which is destabilizing.
An actively controlled rudder could be located ahead of the CG, but cost and complexity normally limit this to things like missiles.

All the above answers are excellent, but I do need to post this:

This the famed HOTOL, SSTO spacecraft. Note the forward vertical stabilizer! In this case I believe the reason for this layout was that during the nose-high entry the rear of the fuselage had basically no airflow. Why they didn't use two wing-tip mounted fins... well you'll have to ask him.

+1 for mentioning HOTOL. A major reason was the much smaller vertical needed for control - this saved precious mass!

Because having the vertical fin fwd of the CG causes static and dynamic instability and requires an augmented flight control system in order to prevent the aircraft from spinning.  Nature has done this kind of arrangement; birds with large beaks such as pelicans and the extinct Pteradactyl used their large heads as rudders during flight and rely on their central nervous system to provide an augmented control system.


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Why are most turbofans tractors, but most propfans pushers?
Turbofans and propfans are, in concept, quite similar: both have a turbojet core, plus one or more additional turbine stages that drive a fan(s) which blows air around the core (this is known as bypass air, because it bypasses the core rather than going through it).  The single defining difference is that, with a turbofan, the fan(s) is enclosed in a large cowling (hence the alternative name "ducted fan", as the bypass air passes through an enclosed bypass duct), while, with a propfan, the fan(s) is left un-cowled (hence the alternative name "unducted fan").
However, in practice, there is one additional, rather odd, difference between most turbofans and most propfans.  Most turbofans operate in the tractor configuration, with the fan(s) placed out in front of the compressors and pulling the engine (and the airplane attached to said engine) through the air, while most propfans operate in the pusher configuration, with the fan(s) aft of the turbines and (surprise, surprise) pushing the engine (and, hopefully, aircraft) through the air.  There are exceptions on both sides; the General Electric CJ805-23 turbofan, powering the Convair 990, operated in pusher configuration, while the Progress D-27 propfan, which powers the Antonov An-70, operates in tractor configuration; however, both are exceptions, and the tractor-turbofans\pusher-propfans rule holds true for the vast majority of engines in both categories.
Why is this?

The Progress D27 tractor is the only propfan I know of that is in production, so I wouldn't consider it an exception.

Please don't follow the habit of marketing to invent new terms for old concepts and continue calling a turboprop a turboprop, including the Progress D-27.

"Most propfans" is a bit of a strong way to put it. The An-70 is the only production propfan aircraft, making the Progress D-27 the only mass-produced operational propfan. So its configuration is the norm.
As for the reasons for experimental propfans using the pusher configuration, it's generally more efficient in aircraft to begin with, as the airflow is accelerated after passing the obstruction (fuselage). In a propfan, it also avoids the need for a long LP shaft.
As for why turbofans near-universally use tractor, the main reason is that the compression provided by the fan takes part in compressing air for the core. I'm less than 100% sure that it's actually worth the extra components and drag for placing the fan forward, but the alternatives are either having a long suction duct or having a separate ring cowling for the fan, none of which are ideal.
The tractor configuration of turbofans also helps a bit with core cooling. That wouldn't apply to a propfan, which needs a cowling for the core either way.

Also, a tail-mounted engine is easier to configure as a pusher than a wing-mounted one.


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How are the services kept running on a plane without an APU?
I have seen several aircraft that do not have an operative APU, so how are lights, air, and other systems kept running?

I think it is not, because there is asked if the parked airliners are always connected, Im asking how to keep the plane running without an APU.

The aircraft is connected to a ground-based supply.
The ground-based air conditioning is connected using a large yellow pipe, and electricity is connected using a set of cables. In the photo below you can see both connections.

image source
In the cockpit, the pilot can select the power source for the aircraft. The proper procedure is to start the APU before disconnecting the ground power supply, otherwise the whole cabin will go dark once ground power is switched off! If you are a passenger boarding, you may have noticed that the cabin lights flicker for a very brief moment. This is when the power source is switched from ground power to APU, as part of the start up procedure.
If the APU is inoperative, things get a little complicated. Typical electricity source include ground-based supply, APU, engines and battery. The battery is only a backup for very essential flight instruments; it is not even capable to
power everything in the cockpit, let alone the cabin. The ground-based supply unit must be disconnected before the aircraft starts moving. So that leaves the engine(s) as our only power source.
However, getting a turbine engine started without an APU is a tricky matter in its own: it requires another ground-based unit to blow air into the engine. The only remaining option is to keep at least one engine running during the turnaround, since the running engine can be used to power up all other engines, at the expense of fuel.

On aircraft like the ATR72, engine #2 can be left running in 'Hotel mode'. This will allow ground activities to continue without requiring ground equipment. It's mostly used for short transits. The key component is a 'prop brake'. It's very noisy though.
Once the aircraft is ready to move, the prop brake will release and the prop will go from stationary to a fast spin almost immediately. Engine number one is then started. It will spool up from sloooww... to fast... to idle (faster).

Generally, aircraft that have no APU or an inop APU will rely on a ground power unit to keep the lights on when parked.

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text:
Is there any information about the Boeing 787 L/N 6 (ex-Mexican Air Force One)?
That Boeing 787 (L/N 6; N787ZA then  XC-MEX) is (was) the Mexican Air Force One, and recently there has been some turmoil about if this is was acquired under lease or if it was a full purchase.
I was roaming around but I did not find any info about the bidding process.
Is there any info about it?
This plane is supposed to be in auction, but I doubt it can if its leased, in any case it can be transferred, but since its a VIP transport I highly doubt any airline or operator would be interested in it.
By the way it is in storage in San Bernardino, California.


text:
Is this opinion on personal computer flight simulators too strict or is it actually true?
A couple of days ago I had a discussion with a commercial pilot and his opinion on personal computer flight simulators were a bit surprising to me.
He said that flight simulators, even with expensive payware aircraft are about as close to the real plane as Call of Duty to real warfare.
He said that most of the time the systems and the switches appear to look similar but key factors when operating those systems are missing, mainly because the manufacturer keeps those details more or less undisclosed. The developers don't even know what to simulate and it makes every single flight simulator just a simple game that bares a slight resemblance to reality but that's about it.
This surprised me to say the least, because I thought the well known, premium payware planes simulate the instruments and the systems very well and all the details regarding those systems are available in manuals that we can easily find online.
But I didn't really know that pilot well so I just accepted his answer, I didn't want to seem rude and try to debate him, but I'm very curious if he told the truth or he just tried to exaggerate. I'm especially skeptic about his comment on the undisclosed nature of flight systems.

Possible duplicate of Can Microsoft Flight Simulator help me learn to fly (or make me a better pilot)?

It's entirely possible the bloke was talking about "fun game" simulators; there is a huge range of "simulators".

I don't think this is an opinion based question. I may have phrased it wrongly, but the pilot's argument was that these simulators can't be realistic and accurate because the manufacturers keep the details of the systems classified. Which I don't really agree with, but i'm not knowledgeable enough on the subject to debate a pilot. That's what I was wondering, not necessarily the realism factor of the flightsims themselves, I'm aware that it's a subjective topic.

"I thought the well known, premium payware planes simulate the instruments and the systems very well" - apparently not

By classified as in military flight simulators?

Then he never heard of things like A2A, PMDG and FSLabs... The FSLabs A320 is only 100$ and can be purchased by anyone. However, it's an exact reproduction of the real Airbus A320, with all Systems working exactly as in real life. This AddOn is even used in professional full-motion simulators.

@Bageletas I think 'classified' was the wrong word choice. I think OP really meant 'proprietary,' which is very different from 'classified.' There's definitely nothing classified about normal civilian aircraft.

@reirab Classified may have different implications, I know it's a word used mainly for military planes and not for civilian aircrafts, but I couldn't really think of any English words that could convey the exact meaning of what he used. (We're not native English speakers). On a second thought confidential would probably be the best word to use in this context.

@Fromthedeep Yes, 'confidential' or 'proprietary' is probably what you're looking for. 'Proprietary' is the more precise term (and, also, 'Confidential' is actually a level of classification, so it's often avoided for non-classified material in situations where it could possibly be confused with the classification level of that name.)

One useful line of questioning might be to find out what he would consider "sufficiently realistic" to be.  He might have a very useful answer, or he may just have the opinion that nothing short of actual flying is anything remotely similar to flying (which is an opinion that may be valid, but isn't of much use for most people).  Hopefully he has a really interesting answer.

I've never played Call of Duty but is it even remotely like warfare to be usable as a comparison against tolerably good flight sims.  Should the pilot rather have compared the flight sim with a tank sim or something similar. My son occasionally plays some tank game that is rudimentary by comparison to even old PC flight sim games.

It isn't true, not as an indictment of the simulator software community as a whole anyway. It may be that your pilot friend doesn't have experience with modern simulators, let's take X-Plane for example...
X-Plane has a "professional use" version, which is simply the regular X-Plane with a commercial license and a few extra features. The underlying software is still the same. X-Plane "for professional use" can be FAA certified as a training device.
This means that the aircraft behaves exactly as would be found in the real world. In fact, X-Plane is sometimes used to verify flight models before more expensive methods are used, and they are relatively accurate. NASA has even written research tools to utilize X-Plane. X-Plane's Garmin G-1000 is incredibly realistic, and X-Plane "for professional use" can drive G-1000 simulator devices.
You can buy other "professional level" simulators for home use like the Redbird Jay which runs the same FAA approved software as the certified simulators. The same is true with Elite Simulator.

FWIW, the guts of FSX are also used in certified training devices. Lockheed markets it as Prepar3D.

I have to disagree.  The pilot's right about PC-based simulators not being realistic, but for the wrong reason.  The problem is that they just can't provide kinesthetic feedback, whether it's varying accelerations, or just reaching out and manually adjusting a control.

@jamesqf Without a full-motion simulator that is correct, however I was judging based on the operation of the controls (what they do), avionics, and flight dynamics. Nothing short of getting in a plane really duplicates the total "feel" of flying.

X-Plan's left turn tendency during the takeoff role is grossly unrealistic (having flown both X-Plan and the real thing), I'd hardly call it "behaves exactly as would be found in the real world"

@SteveKuo -- that's probably a fault of the specific model not quite being dialed in

What flight data is X-plane For Professional Use certified against?

This addresses flight dynamics, but the question is more about systems.  I took that to mean what happens when this hydraulic system is out, or how do the avionics respond to odd circumstances.  System simulation is left largely to the plane add-on rather than to X-Plane itself, so the fidelity of systems modeling is not strictly X-Plane's doing.

Subsonic flight dynamics in X-Plane are superb - given an accurate physical model for the aircraft (ie : a high quality aircraft file) it will fly very close to the real thing.  Most of the aircraft models, however, do not really do as good a job on the cockpit controls.  Flying an X-Plane "747" is like flying a 747-shaped and weighted aircraft with a hobbled generic cockpit.  The flight experience is accurate, and some general IFR stuff is mostly correct, but it's not an accurate representation of a 747 (ie: for type rating purposes) on the inside.

...which is not to say that X-Plane can't get the cockpit controls up to the detail level of a real aircraft, it's just extremely rare (if at all) that you find an aircraft model with that level of type-accurate detail in the cockpit.  The FAA certification for X-Plane, afaik, is valid for a certain number of flying hours of flight training but I don't think that there is anywhere where it is being used for type-rating on specific aircraft.  You still need to certify in a "real" simulator or aircraft for type ratings.

Also, to be clear about what FAA certification means, it's not just the software - the certification applies to a hardware/software combination.  You can't just DIY a hardware setup and pay for the commercial licence - you need to either have the FAA certify the rig you've built OR you  need to go out and buy an existing simulator (which happens to have X-Plane at its core). For example, the Precision Flight Controls B737NG, which is a very good and accurate 737 simulator, and a far cry from a home PC.

@jamesqf it won't give you the full experience of course. But it's quite viable as a systems and procedures simulation.

@UnrecognizedFallingObject this was with a Cessna 172. If they can't get a 172 right then I question the other models

No, that is not true.
There are two concepts here: being close to reality and being certified for training. They are not the same thing.
Certified is in essence an insurance policy. It means "sue me if you find my simulation responsible for a crash, because I am so sure it is accurate". That is why it is so expensive. But just because something is not certified to a high standard, does not mean it is not accurate. It just means no body has spent the resources to verify its accuracy because there is no economic benefit of doing so.

the manufacturer keeps those details more or less classified so the
  developers don't even know what to simulate

Well, not when there is an agreement between the developers and the manufacturer. For example Boeing has a relationship with one of the companies in the aircraft simulation industry. The simulation is so detailed that you can execute abnormal checklists using the real Quick Reference Handbook.
And there are things which do not require propriety materials from the manufacturer. On the other end of the spectrum, a Cessna 172 for example, is so simple and so widely used that it is a matter of how many resources one is willing to put in to get the simulation right. There are products which simulate the combustion engine down to cylinder stroke level, and the inner workings of a combustion engine are well understood.

flight simulators (...) are about as close to the real plane as Call
  of Duty to real warfare.

Even PC-based flight simulators can be used in real pilot training. For example it is useful for learning IFR approaches. Surely certain aspects of the simulation are not as real, but that does not prohibit it from being used as a training aid. Again, note that I am saying it is helpful, not that you can log IFR hours by flying in the simulator. And there are simulators which you can log IFR hours on; they are based on the PC-based software which I am talking about.
Let's talk more about certification. There are various levels of certification, covering different aspects of the simulation. For example there are simulators which focus on navigation and instrument procedures, and they are certified by the aviation authorities for such tasks. They are not, however, certified for practicing say an engine bleed failure.
The Level D simulators, which presumably your commercial pilot got his training in, has a very high standard and low tolerance. They are called "Level D" because there are Level A, Level B and Level C simulators. Level A is more relaxed and does not require a motion system for example. Level D is at the top of the game and they are the very best simulator one can get their hands on.

every single flightsim just a simple game that bares a slight
  resemblance to reality but that's about it

You can take the below statement as a personal account or as a bluff on the internet: after my first introductory flight at a flying school, the staff asked if I have heard of PC-based flight simulators and suggested that I learn and practice some basic stuff in the sim while pursuing my PPL. That was before she learnt I would do barrel rolls and hammerheads in the sim...

flight simulators (...) are about as close to the real plane as Call of Duty to real warfare. -- Even PC-based flight simulators can be used in real pilot training ... Even Doom II can be used in real military training.  Doesn't mean it is in any way accurate to reality, however, just that the trainers felt there was at least one useful lesson to learn from it.

well said, Kevin. I had a similar experience to you but in reverse. Instructor asked if I had pc simulator experience, I told him I did. After some questioning he then decided to let me do more than he'd normally would during a first flight and he was impressed with my grasp of the material. Can it replace actual flight experience? Obviously not. But it can help familiarise yourself with procedures and even help practice cross country vfr flights if your scenery is detailed enough

There is a whole spectrum of flight simulators. These range from mobile apps to room-scale 3D professional simulators. The difference lies in the purpose of the software, i.e. fun vs training. I believe your friend is referring to standard flight simulators such as X-Plane and FSX.
In this case I would agree with him, because it is impossible to simulate every possible failure that can happen in flight. For example, a solder joint can break in flight, causing very strange behavior. Also, the interactions between components internally, for example the XNDR getting the mode S data from the other components will not be simulated, but will be a variable passed to a different module.
Modern avionics is based on Line Replaceable Units, which are sent back to the manufacturer when they fail. This means that the operator of the airplane does not know what is inside in most cases. They do not need to know, because all they do is remove/replace the LRU. The soldering of components is left to the manufacturer.
Next up is the version of the LRU. The developer might have coded a certain model of LRU, which may have changed since the launch of the simulator. Pilots may be flying model 2.3, while the sim still features model 1.1. Model 2.3 may have additional options that model 1.1 does not have, or it may be modified or present itself in a different location in the cockpit. There are fleets in which the avionics package differs from tail to tail, for the same type of aircraft. This configuration issue is very hard to program, because you would have to code every version of a LRU separately.

Disagree. You may not be able to perfectly simulate every single failure that can happen, but you can train with many many types of failures that would be just too dangerous to train with in a real airplane. Even if it is not perfect, that kind of experience can make flight sims way more than just "fun."

Agree. The simulated behaviour is not held to any objective scrutiny.

There are many levels of simulators; and not all are created the same. I can somewhat relate to what the pilot has said.
I used to fly exclusively a very high ranked commercial flight simulator (on my personal computer) with a dedicated yoke and throttle setup. This was for the 737.
Then I had the opportunity to train as a "tour guide" for a flight experience company, which uses Pacific Simulator's equipment.
Thinking "how hard could it be" and feeling confident on my procedures and instrument knowledge, I signed up and then was taken into the cockpit and greeted by this (picture from pacific simulators):

I knew what everything did, but here is what I didn't know and you can't know unless you've sat in a cockpit

The fact that the chair moves up and back and not in a straight direction.
Three point seatbelts are not fun
The brake pedals are difficult to reach if you are short (I'm 5'8")
The yoke ... its difficult to hold on to and has some serious resistance.
The gear lever, you have to pull out and then lift (or drop it).
The trim wheel actually spins
Overhead lights can get hot.
Ground steering is only on the left side (?!@)
Flap lever gates are very rigid.
Keeping on the centerline isn't as easy when you have a stereoscopic view.

Many more things such as the level of noise, etc. All this on a static simulator. I can only imagine how wild it would get on a full motion simulator like the ones they have at airline training centers.
Once I got past the entire physical experience - the airplane performed exactly as it did on my home computer - except for one small detail, at full flaps the simulator model tends to rise (due to the increase lift) and you have to compensate by some yoke forward pressure.
On the home PC, maybe it was the autopilot taking care of it, but I could not discern this behavior.
Other than that, and the overwhelming sensation (I was sweating after my first 40 minute flight) its the same...if you can discount the entire dexterity of the simulator experience.
So yes, in many ways your home PC setup is a simple facsimile of the real thing and many of the physical, tactile properties you will never experience unless you sit in an actual cockpit.
As a side effect of this experience, my respect and love for the plane and its pilots increased even more.

You never noticed that the trim wheel spins and ground steering is only on the left in a nornal PC simulator? One can noticed that there pretty easily.

The wheels didn't spin on mine - well I suppose they did if you used the 3D view, I was using the instrument view 99% of the time.

"The trim wheel actually spins" I take it you didn't expect this, which for me raises the question: What did you expect it to do?

I didn't expect it to spin on its own (perhaps I should have clarified that initially)

Certainly fair enough, and makes much more sense than the way I interpreted your original comment.

Also I forgot to mention, some switches are heavier than others, probably to avoid accidental activation and for muscle memory. The landing light switches come to mind.

First, the ins and outs of avionics are hard.  This might be a trivial difference for an amateur trying out an old Cessna 172, but at the other end of the spectrum, if you're a real pilot trying to simulate procedures on something complex like an F-35 or G1000Nxi, you care about lots of little details.  Thousands of them. Things like:

ForeFlight integration
equipment failure scenarios
aerodynamics accuracy
the hundreds of corner cases that pop up

Avionics requirement documents are thousands of pages about how things should transition from on to off, nuances of on-ground vs engines-on vs moving vs weight-on-wheels, maximum limits, mode interactions, message displays, redundancy scenarios when one piece of equipment fails, etc.  They're complicated enough that there are corner cases that get missed and heated discussions over seemingly tiny implementation details.
Pilots don't care about these details because pilots are uppity; it's because they're professionals and their lives depend on knowing what to do when the compressor stalls while a different aural warning is going off.
Can you get a reasonably accurate simulation, sufficient to practice things like instrument procedures?  Yes.  But to get accuracy you need:

Serious investment and attention to detail (even some paid products have missing features and inaccurate dynamic performance)
At least a manual, if not technical data, from all the avionics developers for the plane
Accurate aerodynamics for the plane itself
A good understanding of performance behavior and issues (e.g. how much does altitude change when you deploy the flaps while the autopilot is set to maintain altitude?)

Additionally the "feel" of flying a plane is missing in home simulators.  You can't feel the plane moving, making maneuvers and especially takeoffs and landings very difficult. This was covered extensively in this question on how useful MS Flight Simulator is., and I feel like you care more about the avionics than just the overall simulation usefulness.

If a professional pilot states from experience that they are unrealistic, it must be true: that is the closest reference we'll ever have for the PC-based programs, since they are not normally referenced to actual flight data. Certification of a device means that they have been held to scrutiny and that proof must have been provided at one stage that the behaviour of the system/flight model is realistic. For an uncertified PC-program, who knows? it could be realistic, or not...sales are most important, cool graphics, good sounds etc.
Since Microsoft started to market a PC game called Flight Simulator, there is a bit of confusion about the term. There are:

Flight simulators, used for training professional pilots. Some devices are used for entertainment purposes as well: you can buy your dad a ride with a certified instructor for father's day.
PC-based programs, for the general public. These can be used by professionals as well in the comfort of their homes.

The word Flight Simulator exists since almost a century, when Ed Link built his first device for instrument flight training. This became an industry: in flight simulators pilots can be trained in situations that would be dangerous in the air. Emergency situations can be learned by rote and drilled in until all actions are carried out rapidly; an engine fail during take-off can be presented and the appropriate actions can be carried out, without any personal danger.
The industry bears a heavy responsibility: if a crash occurs due to inappropriate pilot actions that were trained in a simulator, the manufacturer of that device faces huge costs, both in money and in human lives. So the aviation authorities demand that the manufacturers demonstrate that what they have made is like the real aeroplane: the response of the simulator must match that of the real aircraft. And that is a big cost driver for simulators for professional use: you must have a recorded response of the real system or aircraft manoeuvre in order to match with the simulator.
But not all tasks need to be trained at the same frequency, and one way of making simulators less expensive is to verify them only for certain tasks. A navigation trainer must have the navigational systems that respond like the real ones - the best solution is to use the original system on board of the aircraft, and simulate the behaviour of the aircraft when it flies on autopilot, which is a calm, controlled flight path without the quirky responses for hand-flown tight manoeuvres. Part Task Trainers have been certified for decades as well.
Image source
The classical distinction between flight simulation and part task system trainers has disappeared in the last two decades: a Flight Simulator is now any program that shows an inside view of a cockpit, some out of the window movement as a function of a joystick input, and lights and buttons that act in a way that seems familiar to pilots. Microsoft said that they are Flight Simulators. Some of the PC programs are used in Part Time Trainers to simulate part of the response of a similar aircraft, and the manufacturers can then claim that they are FAA Certified. It does of course not mean that the reaction of the program is measured against those of the real aircraft, like Full FLight Simulators need to be.
The distinction is still:

Is the simulator certified. Not the software in general, but the training device.
For what tasks is it certified. Systems training only, or flight as well?
If for flight, to what level? Cruise and fair weather, or the full effects of turbulence, windshear, ground effect? Can landings be trained in the simulator? Then we're talking about a Full FLight Simulator, and I can assure you that none of the X-planes, Microsoft games, or FlightGears are powering those.

The commercial pilot you spoke to has had extensive training in professional, full motion, Level D simulators with an incredible amount of proven and certified realism. He compares that with the PC programs called Flight Simulator, some of which are used for some out-of-the-window view for some part task trainer. And he would be correct in stating that the realism of the commercial PC games available for USD 100 is very poor. His opinion is the truth, and how can it not be: a full data package for a commercial airliner that a Level D Full Flight Simulator is certified against, costs between 2 and 10 million USD. X-plane is really not going to spend that.

"If a professional pilot states from experience that they are unrealistic" it must be his personal opinion. OP came here to get other opinions. That opening qualifies this as "not an answer".

I understand what your pilot friend is saying and to a certain extent I agree with him.
A desktop flight simulator like FSX, X-Plane, Prepar3D, etc. is a far cry from a level-D full motion simulator manufactured specifically for a particular aircraft with a complete user interface, systems, accurate avionics, etc.  But I don’t think it is then fair to say that a desktop PC flight simulator is unrealistic.
I’ve written another post on this subject before but it bears repeating.  Desktop flight sims are entertainment products built with a level of realism which allows them to be quickly converted for flight training.  They do model basic flight dynamics and other aspects of flying very well, while other areas are lagging, for a number of reasons, including ease of use by neophytes and more concentration on the more commonly used aspects of flight for simming.
All sims have their good points and their limitations.  I’ll take FSX as an example.
Positives:

Economical training program
Excellent basic flight dynamics
Very good instrument trainer.
Allows the user to sample the flight characteristics of numerous kinds of aircraft economically.

Drawbacks:

Engine dynamics are only realistically tailored for normally aspirated piston engines.  It does not model turbocharged piston engines, turboprops, or turbojets well.
Serious control lag from time of input to response of control surfaces, even with control axes null zones set to zero.
Systems are modeled at a basic level only and requires additional add-on in payware aircraft to make them realistic.  For example FSX’s basic electrical system doesn’t replicate the emergency backup battery system used on their G1000 installation for their high wing single engine line.  The Acceleration F/A-18 Hornet is laughably unrealistic.
Basic avionics flat out suck, including their G1000 system, replicating only a fraction of the features nor doing it accurately compared to the real thing.
Aging navigation databases make it increasingly unrealistic for use as a training device.
Air traffic control is limited and somewhat like a human having a conversation with a Barbie Doll.
Edge of the envelope flight characteristics, including aerobatics and spins are not modeled well and are docile and clunky compared to real life.  The FSX Extra 300S is a dog compared to the real aircraft.
Weather hazards are not modeled correctly and are there only for aesthetic reasons.  You can fly an Airtrike into a raging thunderstorm with zero risks aside from getting tossed around a little.  Try that in the real world and you’re a dead man.

Many of these problems can be alleviated using add on realistic payware aircraft and weather add-ons.  There is also avionics payware which dramatically increase the realism of the avionics used in the game.
I have used FSX for a great deal of my flight training and it has dramatically improved my skills as a pilot.  The same mistakes I make in FSX, I will make in the real thing as well!

This is a subjective question which gets to the problem of what does "realistic" mean.
I kind of agree that flight simulators, either in their controls or their flight characteristics, are not really realistic substitutes for flight except for limited purposes. Here are some of the differences:

In many cases, instruments and controls are complex devices that cannot easily be simulated by a computer. For example, even very simple instruments like altimeters and vertical speed indicators behave much differently in a real plane than in a simulator. Real instruments have weird lag characteristics and respond to gusts and other transient conditions. The real instruments are much more erratic than what you see in a simulator.
Large commercial aircraft have complex systems system like flight management computers that have large amounts of proprietary software that a PC simulation has no ability to accurately simulate. For example, all FMCs have engine performance models written by the engine manufacturer (GE, Pratt & Whitney, etc). These models are extremely complicated and highly proprietary (secret).
Simulators do not accurately model the way a plane interacts with the air. For example, glider pilots do not even use simulators like X-Plane at all for this reason. They use specialized simulators like Condor.
No simulator, either X-plane or Condor, accurately represents gusts and other erratic air movements the way they are in real life. Landing in real life is much more difficult than in a simulator because turbulent air conditions near the ground often require rapid control inputs to land smoothly; none of this is modeled accurately in simulators I have used.
Simulator controls feel nothing like real controls. Small aircraft use spring loaded yokes and large ones use hydraulics. The plastic rudder pedals you can buy for a simulator feel absolutely nothing like real rudder pedals. Also, the plastic ones lack toe brakes, so the whole braking experience is completely different in a plane than in a simulator.

There is a difference what can be simulated and what the authors want to simulate. Erraticc instruments, lags, different resonses for different frequencies of turbulence... that all can be simulated in a straghtforward way. It is just a a matter of the add-on aircraft authors wanting to do that. The issue is similar as with navigational instruments. Normally, a PC sim displays an accurat position. But a good INS add-on will include random drift or other sources of uncertainty. Similarly for NDB and others.

If you look well, there are better pedals available. Not plastic and including breakes. See, for example, http://pedaly-happy-mzm.webnode.cz/fotogalerie/ Serious simmers use serious hardware.

It will depend of what do you want to learn from your PC Based simulation.
That is also why all type of regulation have different type of simulator qualficiation (ICAO, FAA, EASA, CAAC, ...)
If we look at the definition from EASA FSTD(A) 2012 (unfortunately the table from ICAO 9625 Ed4 is better but the document is not available freely on internet):

Appendix 1 to CS
  FSTD(A).300
  Flight Simulation Training Device Standards
  This Appendix describes the minimum full flight simulator (FFS), flight training device (FTD),  flight  and navigation  procedures  trainer  (FNPT)  and basic instrument  training devices  (BITD)  requirements  for  qualifying  devices  to  the  required  qualification levels. Certain requirements included in this CS should be supported with a statement of compliance (SOC) and, in some designated cases, an objective test. The SOC shall describe  how  the  requirement  was  met.  The  test  results  should  show  that  the requirement  has  been  attained.  In  the  following  tabular  listing  of  STD  standards, statements of compliance are indicated in the compliance column.

Source:
EASA CS-FSTD(A) p9 to 25: https://www.easa.europa.eu/sites/default/files/dfu/CS-FSTD(A)%20Initial%20Issue.pdf
That table will help instructors to know which kind of simulator can be used for each kind of exercises. So FFS are not the only kind of simulator used by training centers to teach and to get a Type Rating.
The limitation of a PC Based simulation like X-Plane or FSX, is not necessarily in the representativeness of the airplane but the limitation of information about the aircraft itself. Even with the good aeromodel (like the one in x-plane) you need data to compare the behavior of the aircraft with your aeromodel. It is even possible that the Airplane Manufacturer doesn't extract this kind of data from the Test Flights.
The other limitation will reside in the systems themselves. Without having the right documentation how do you want to reproduce the FWS of an A320 even if you have the FCOM has a reference. There is way too much logics behind it to retro-engineer it from a document like that. Same for any avionics, G1000, HNY suite, ....
But the PC Based simulation is not necessary totally useless. For example, to locate the right place of each pushbuttons, levers, switches, ...
It can also help (if the system is well simulated enough) to learn the basic of entering a flight plan. Which kind of information are important and so on.
But definitely from a piloting point of view, following the accuracy of the simulation, it can easily start to become negative training if something wrong happen and the behavior from your simulation is not the same as the real avionic.

Negative transfer is defined in the context of this paper as the transfer from one cockpit to another--of different design or configuration--of habits or responses which were appropriate in the former but are inappropriate in the latter, thereby posing a threat to flying safety. This danger has been demonstrated not only experimentally but also in a number of aircraft accident investigation reports. As new aircraft become available to the commercial, military, and private sectors and pilots consequently must transition from older to newer models, the phenomenon of negative transfer becomes increasingly significant. To illustrate the concept of negative transfer and aviation, the author compares the cockpits of two USAF aircraft and how their differences could adversely affect pilot performance. Recommendations are then made on ways organizational flight surgeons can minimize the negative transfer threat to aviation.

Source:
 https://www.ncbi.nlm.nih.gov/pubmed/7159345

authors: Vladimir F Героям слава

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Can aircraft depart/arrive after another aircraft has sprayed snow on the runway?
Does snow spray affect runway surface friction? The weather was bitterly cold on March 18th, 2018 and Birmingham airport was covered with snow. As you can see in this video, an A380 sprays snow on the runway when arriving and departing.

(Frame from video)

Aircraft can land in snowy weather without a problem, the fact that there is a little bit of snow on the runway does not change that. The amount of snow can cause problems if it too deep and will interfere with the engines/landing gear struts etc.
The snow sprayed on the runway by the A380 is just a small film and no problem for aircraft to take-off and land on. The runway can become a bit more slippery decreasing the braking performance of the aircraft.


text:
Why is the 737 MAX 7 selling so poorly?
The 737 MAX 7 is the smallest of the four major variants in Boeing's 737 MAX product line; it is intended as the successor to the highly-successful 737-700, and features a higher fuel efficiency, considerably greater capacity, and increased range compared to the 737-700.  Yet it is selling very poorly, with only 58 orders so far - and 23 of those 58 orders, from MAX 7 launch customer Southwest Airlines, have been deferred until the mid-2020s, raising the possibility that Southwest might cancel those 23 orders entirely.
Why are the airlines which enthusiastically jumped at the -700 balking at its successor, despite its being the longest-ranged 737 ever (the MAX 7 can fly for 7,130 kilometres before it needs to refuel), thanks to its increased fuel efficiency, and having a capacity of 138-172 passengers, as compared to the -700's 138-140 passengers?

I disagree that this question is based on opinion. There are 100 customers for the MAX and there are reasons that only a few have ordered any of the -7. We may not have all the information but we should be able to provide a reasonable answer. We have similar questions like: Why is Airbus proceeding with both the A330neo and A350 XWB?

You may clearly indicate why you think the sells are poor. This may be done by comparing the current one to other similar aircrafts (other B737, A320, any other aircraft with similar capacity). In short, you should not say "poor" without comparing it to comparable figures if you don't want your question to be closed as "opinion-based"

Keep in mind Southwest has a very long history of being hte launch customer for the latest 737 model. Going clear back to the Classic models.

While Boeing has delivered over 1,000 of the -700 version, popularity has gone down more recently. There were 101 delivered in 2007, and it declined sharply from there. Only 18 have been delivered since 2015, compared to 1,300 of the -800. So the recent sales performance of the two is not that different. The direct competitor is the A319neo, which has a similarly low number of orders.
There is new competition from the Bombardier CS300 (now Airbus A220-300), which carries 130 seats in a 2-class configuration, and the Embraer E195-E2, which carries 120 in a 2-class configuration. The 737-7 is a smallest version of the family so some of the operating costs are fixed by the larger models. Although the Bombardier/Airbus and Embraer planes have fewer seats, they are newer designs and the smaller size also helps to bring down the price and operating costs.
The 737-7 does have some advantages of being the smallest of the family including having the most range with standard fuel tanks. Airlines using the 737-700 version for its extra range might find that the 737-8 has the range they need while also carrying more passengers. Boeing also made the -7 a bit longer than the -700, so airlines might find that for the smaller difference they might as well just go with the larger version.

The 737-700 is not the Max7 in the question.

However, the 737-7 is.

There are two reasons: the market changed, and seat economics favor larger aircraft.
The NG models were designed in the early 1990s, before much of the dramatic change in the air transport market wrought by deregulation and ascendancy of LCCs. Southwest for example, was using high frequency of narrowbody aircraft to attack the network carriers and drove the extinction of widebodies in domestic US air travel. Since the early nineties, airline traffic has more than doubled depending on how you count, and there is a maximum frequency that is appealing to travelers. If you have four flights a day on a particular route and you double traffic, you might decide that six is enough and use larger aircraft.
This is what Southwest is now doing, replacing -700 aircraft with Max8s. The Max8 acquisition and operating cost is only about 10% higher than the -700, but its passenger capacity is 25% greater. The math makes the smaller aircraft unusable, given that market demand now supports the larger aircraft. Ryanair came along later than Southwest and went straight to the lower seat cost of the larger aircraft. This is why even smaller aircraft like the Cseries are in trouble, forcing Bombardier to sell half of the program to Airbus for nothing.

The Cseries Airbus deal seems to be more to get assembly facilities in the US with the duty problems that they were facing.

@GertvandenBerg The Cseries had been in trouble due poor sales for years with only 375 orders in the nine years it was offered. 75 of those were tied up in the Delta dispute with Boeing, who was trying to kill the model off for good. Bombardier claimed they would get half of their projected 6000 units over 20 years, ie. 3000 units. Only 300 clear orders in nine years was a fifth of their plan, and they were bleeding cash. They had tried to sell some portion to Airbus a year earlier and were rebuffed. By late 2017 they had no choice and gave it away.

What's an LCC? xxxx

@rclocher3 Low Cost Carrier

There is nothing wrong.
Boing is hedging its bets by offering 4 737-MAX variants. Aircraft manufacturers doubtlessly ask their customers for their preferences, yet neither the manufacturers nor the airlines can gauge which aircraft will fit the market in 5 or 10 years.
There are also specific Airbus variants that sell poorly compared to their sibling-variants, e.g. the A-330 800/900 variants, which have 10 respectively 238 orders (by August 2019).
As long as an aircraft manufacturer offers a large enough variety of aircraft, either with distinct aircraft or aircraft variants, it will satisfy the needs of the airlines, which are hard to predict.


text:
What is this abandoned airport between Montague and Rothbury, Michigan?
It appears to have had two intersecting paved runways, each very roughly 2000 feet long (give or take); the one that runs closer to north-south is still legibly numbered as runway 17/35, but the other runway is in much worse condition (suggesting that it was closed some time before runway 17/35), and its pavement is too broken up for me to make out the numbering.  Runway 17/35 has considerably larger turnaround areas at both ends than the other runway does.  There is a cleared strip extending for approximately 400 feet past the southern end of runway 17/35.
West of the intersection of the two runways, there appears to be a dilapidated apron, with taxiways connecting it to both runways; immediately north of the apron, there is what could be the remnants of a collapsed hangar, or could be something else entirely (there is another area of junk just to the southwest of the apron).
Google Maps link to location of the former airport here.
Google Maps screenshot showing the mystery ex-airport:

I'm not sure you have enough tabs open...

Looks like it was a private field.  So not a lot of news articles about it closing.

The other runway being 3/21.  Only slightly shorter but with much bigger tree-clearance issues.

It's nowhere near the record for tabs open @RonBeyer, that's somewhere over 2000 IIRC. Don't let him shake you Sean, you can never have enough tabs!

@GdD: I think I'll pass on that, at least for now; Chrome gets dog-slow when I have hundreds of tabs open.  (BTW, I think my personal record is 277 tabs open simultaneously.)

I think that's too much even for me @Sean.

My family complains when I have >10 open. (Which is my normal minimum)

Looks like there is a mentioning of this airport in 1966 about a glider landing there. If so, it is an old airport with long history. And there is Sikkenga road very close to it, so the airport probably used to be easily accessible in the past.

@GdD: I've since gotten up to over 530 (it's currently back down to 140 as I type this).

The airport is Ottiger Airport (2MI6) which is closed indefinitely. I cannot find any information on when it was closed or for what reason. The last update date that I can find for the charts is August of 2006, which is probably when the airport was closed.
Apparently there is one person who is trying to revive the airport for private use according to this post on Facebook.

I wish I had more information to add but my comments on other questions have been deleted. I feel this would have been better as a comment.

Facebook page with some pictures.  https://www.facebook.com/Ottiger-Field-since-1950-188908855056078/ . Includes a photo of a tree and a comment about the state withholding a license due to it.  Can't find any corroboration.

That is Ottiger Airport.  I flew out of there for 10 years.  It is situated between Fruitvale Road on the South, Meinert Park Rd on North, and Sikkinga Road on the West. There was one paved runway that was 2600 ft. long and one shorter runway about 1800.  There were two hangers and a gas pump.  during the 60s & 70 there were about 7 planes there year round and many visitors during the summer from everwhere even a Dornier from Germany one summer, I knew Mr. Ottiger very well as he also was one of my fishing partners.  The shorter runway was made of oiled gravel and there was only one paved runway which was done by the army at Camp Claybanks approx. 5 miles north of there.

It looks to be Ottiger Airport 2MI6
Normally with these kinds of airports they should show up on aeronautical charts as closed or abandoned to avoid any confusion with other airports (this way a pilot doesn't accidentally land on the wrong runway) but this one doesn't show on this online Aeronautical Chart SkyVector. Presumably because there aren't any other airports near 2MI6.

The description for "abandoned" states that it's normally used for ex-airports with "at least 3000' paved", which could be the reason it doesn't show up on the chart (both of Ottiger's runways are (were?) under 3000 feet).

2MI6, Ottiger Airport, is currently under rehab for private use. The Michigan airport inspector shared his past inspection reports, which have been posted on Facebook- Ottiger Field since 1950. The license was not renewed due to deterioration of the runway surface, lack of Displaced Threshold (DT) markings, and refusal to remove a majestic oak tree. Note that private use has a lower threshold of setbacks, etc. It seems the field was operated with commercial activity (instruction and fuel sales) for some time. Absentee owner left it to users to maintain, which seemed to decline and eventually stop about 2004. Expect it to be listed for sale shortly.

Never was identifier 2MI6 - that is another private field in the center-north of lower Michigan. Ottiger was C26 before public license lost in 1988.

should probably just update your previous answer rather than creating a new one